JP Patent Publication 2014-9721A discloses one of the known rotation transmission devices used to selectively allow and prohibit transmission of rotation from an input shaft to an output shaft.
The rotation transmission device disclosed in JP Patent Publication 2014-9721A includes a tubular housing of which both ends are open; an input shaft having one end thereof received in the housing; an output shaft arranged coaxially with the input shaft; an inner ring provided at the portion of the input shaft received in the housing; an outer ring provided at the portion of the output shaft received in the housing and surrounding the inner ring; pairs of rollers, each pair being received between a cylindrical surface on the inner periphery of the outer ring and one of cam surfaces on the outer periphery of the inner ring; and a roller retainer retaining the pairs of rollers.
The roller retainer comprises two split retainer portions supported so as to be rotatable relative to each other. The two split retainer portions are movable between an engaged position where the pairs of rollers are engaged between the cylindrical surface on the inner periphery of the outer ring and the respective cam surfaces on the outer periphery of the inner ring, and a disengaged position where the pairs of rollers are disengaged from the cylindrical surface and the cam surfaces.
The rotation transmission device further includes an electromagnet as a driving source for moving the two split retainer portions. The electromagnet is mounted at the end portion of the housing of the rotation transmission device on the side of the input shaft.
This rotation transmission device further includes, as bearings for rotatably supporting the input shaft and the output shaft, a first bearing mounted between the electromagnet and the input shaft, a second bearing mounted between the end portion of the housing on the side of the output shaft and the output shaft, and a third bearing mounted between the inner ring and the outer ring. The first bearing, the second bearing, and the third bearing are all single-row deep groove ball bearings.
This rotation transmission device is used, for example, in a steer-by-wire type vehicle steering assembly. A steer-by-wire type vehicle steering assembly converts the steering angle of the steering wheel when the steering wheel is operated by a driver to an electrical signal, and steers right and left wheels based on the electrical signal. The rotation transmission device is mounted in the rotation transmission path of this steer-by-wire type vehicle steering assembly between the steering wheel and a steering actuator configured to change the steering angle of the right and left wheels. The rotation transmission device has a function as a backup clutch which, during the normal state, prohibits transmission of rotation between the steering wheel and the steering actuator, and which, in an abnormal state, such as if power is lost, allows transmission of rotation between the steering wheel and the steering actuator.
In mounting the above-described rotation transmission device, the input shaft is connected to a shaft on the side of the steering wheel by a shaft coupling. The output shaft is connected to a shaft on the side of the steering actuator by a shaft coupling, and a flange provided on the outer periphery of the housing is fixed to a portion of the vehicle body (such as a partition wall between the dashboard and the engine room) by, e.g., bolts. Thus, when using the above-described rotation transmission device, it is necessary to design the vehicle body such that the flange on the outer periphery of the housing can be fixed to a portion of the vehicle body.
The inventors of the present invention considered the possibility of omitting the flange on the outer periphery of the housing. In particular, they considered the possibility of supporting the rotation transmission device only by connecting the input shaft and the output shaft to the shaft on the side of the steering wheel and to the shaft on the side of the steering actuator, respectively, while not fixing the housing by the flange as in the conventional arrangement. If it is possible not to fix the housing by the flange, it will be possible to simply replace conventional shafts of a steering device to which no rotation transmission device is connected, with shafts to which the rotation transmission device having no flange is connected. This improves freedom of design.
However, if the housing is not fixed in position by the flange, it was discovered that the following problem arises.
In particular, if the housing is not fixed in position by the flange, the rotation transmission device is supported by the shaft connected to the input shaft on the side of the steering wheel, and the shaft connected to the output shaft on the side of the steering actuator. In this state, since the input shaft and the output shaft are supported at only three locations, i.e., by the first bearing mounted between the electromagnet and the input shaft, the second bearing mounted between the end portion of the housing on the side of the output shaft and the output shaft, and the third bearing mounted between the inner ring and the outer ring, the axes of the input shaft and the output shaft tend to be inclined relative to each other (that is, misalignment tends to occur therebetween). If the axes of the input shaft and the output shaft are inclined relative to each other, the relative position between the inner ring provided on the input shaft and the outer ring provided on the output shaft changes, thus destabilizing the behavior of the rollers mounted between the inner ring and the outer ring (such that the rollers could remain engaged when they are supposed to be disengaged, or could become engaged when they are not supposed to engage).
An object of the present invention is to provide a rotation transmission device of which the housing need not be fixed in position by a flange, and of which the engaging elements between the inner ring and the outer ring are stable in behavior.